This invention relates in general to a fuel cell power plant having an integrated manifold system, and deals more particularly with an integrated manifold system of a fuel cell power plant which uniformly delivers input reactants to the fuel cell power plant while reducing the overall weight and volume of the fuel cell power plant.
Many types of fuel cells are known in the art, such as solid oxide, molten carbonate, phosphoric acid and proton exchange membrane (PEM) fuel cells. Fuel cells generate electricity by directly converting chemical energy to electrical energy. In a typical fuel cell, an electrolytic medium separates an anode and a cathode. A voltage is produced between the anode and cathode when a fuel is introduced to the anode, an oxidant is introduced to the cathode and the cell is maintained within the correct temperature range. The electrolytic medium allows an ionic species to travel between the cathode and the anode.
The products generated by fuel cells are relatively simple and benign, typically including water and carbon dioxide, thus minimizing environmental concerns. In contrast with fossil fuel based power sources, such as the internal combustion engine, fuel cells are simpler, quieter, non-polluting and have high operating efficiencies. For these and other reasons, fuel cells are considered promising power sources for the future.
In practice, however, operation of a fuel cell stack can be complex. Considerable hardware may be required to support a fuel cell stack, which is typically comprised of a plurality of individual electrically integrated fuel cell assemblies. Such hardware can include a thermal management subsystem for maintaining the fuel cell stack at the proper temperature, a water management subsystem for handling water generated as a reaction product of operating the fuel cell stack and for maintaining proper humidity throughout the power plant, a fuel subsystem for processing and delivering the fuel reactant to the fuel cell stack, and a blower for delivering the oxidant to the fuel cell stack. Taken as a whole, a fuel cell stackxe2x80x94or a plurality of electrically connected fuel cell stacksxe2x80x94and its operating subsystems comprise a typical fuel cell power plant.
As understood by one of ordinary skill in the art, the components and subsystems of a fuel cell power plant can vary depending on the applicationxe2x80x94a phosphoric acid stationary power plant for industrial use will differ from a mobile, typically (PEM), power plant. Furthermore, a mobile PEM power plant that can be provided with hydrogen as a fuel reactant can differ considerately from a PEM plant for installation in an automobile, which can be required to include a subsystem for producing hydrogen fuel from gasoline. In general, a fuel cell power plant includes those subsystem components necessary for the application for which the power plant is to be used, and that are appropriate to the type of fuel cells incorporated by the fuel cell power plant. In order to control the temperature within a fuel cell assembly, a coolant is provided to circulate about the fuel cell assembly, usually water.
Electrochemical fuel cell assemblies typically employ hydrogen as the fuel and oxygen as an oxidant where, as noted above, the reaction by-product is water. Such fuel cell assemblies may employ a membrane consisting of a solid polymer electrolyte, or ion exchange membrane, disposed between the two electrodes formed of porous, electrically conductive sheet materialxe2x80x94typically carbon fiber paper. The ion exchange membrane is also known as a proton exchange membrane (hereinafter PEM), such as sold by DuPont under the trade name NAFION(trademark), has a catalyst layer formed thereon which results in a membrane-electrode interface that promotes the desired electrochemical reaction.
In operation, hydrogen fuel permeates the porous electrode material of the anode and reacts with the catalyst layer to form hydrogen ions and electrons. The hydrogen ions migrate through the membrane to the cathode and the electrons flow through an external circuit to the cathode. At the cathode, the oxygen-containing gas supply also permeates through the porous electrode material and reacts with the hydrogen ions and the electrons from the anode at the catalyst layer to form the by-product water. Not only does the ion exchange membrane facilitate the migration of these hydrogen ions from the anode to the cathode, but the ion exchange membrane also acts to isolate the hydrogen fuel from the oxygen-containing gas oxidant. The reactions taking place at the anode and cathode catalyst layers are represented by the equations:
Anode reaction: H2xe2x86x922H++2e
Cathode reaction: 1/2O2+2H++2exe2x86x92H2O
Conventional PEM fuels cells have the ion exchange membrane positioned between two gas-permeable, electrically conductive plates, referred to as the anode and cathode plates. The plates are typically formed from graphite, a graphite-polymer composite, or the like. The plates act as a structural support for the two porous, electrically conductive electrodes, as well as serving as current collectors and providing the means for carrying the fuel and oxidant to the anode and cathode, respectively. They are also utilized for carrying away the reactant by-product water during operation of the fuel cell.
When flow channels are formed within these plates for the purposes of feeding either fuel or oxidant to the anode and cathode plates, they are referred to as fluid flow field plates. These plates may also function as water transfer plates in certain fuel cell configurations. When these plates simply overlay channels formed in the anode and cathode porous material, they are referred to as separator plates. Moreover, the plates may have formed therein reactant feed manifolds which are utilized for supplying fuel to the anode flow channels or, alternatively, oxidant to the cathode flow channels. They also have corresponding exhaust manifolds to direct unreacted components of the fuel and oxidant streams, and any water generated as a by-product, from the fuel cell. Alternatively, the manifolds may be external to the fuel cell itself, as shown in commonly owned U.S. Pat. No. 3,994,748 issued to Kunz et al. and incorporated herein by reference in its entirety.
The catalyst layer in a fuel cell assembly is typically a carbon supported platinum or platinum alloy, although other noble metals or noble metal alloys may be utilized. Multiple electrically connected fuel cell assemblies consisting of two or more anode plate/membrane/cathode plate combinations are referred to as a fuel cell stack. A single fuel cell stack is typically electrically connected in series.
Often, the particular application for which a fuel cell stack is utilized demands a system voltage which exceeds the capacity of a single fuel cell stack, due primiarily to the structural limitations on the size of such a fuel cell stack. That is, for a single fuel cell stack to generate extremely high voltages, the length of such a fuel cell stack would become impractical, leading to possible structural deformation of the fuel cell stack as a whole. In order, therefore, to compensate for these situations of high voltage demands, two or more fuel cell stacks may be utilized in combination to form the electric generating portion of a fuel cell power plant.
Multiple, operatively connected fuel cell stacks are particularly useful in various transportation applications requiring high voltages. There are, however, additional concerns associated with utilizing multiple fuel cell stacks in such applications, especially where the weight and volume of the constructed fuel cell power plant is of primary importance. In addition, when multiple fuel cell stacks are utilized, it becomes increasingly difficult to ensure the uniform distribution of fuel and oxidant reactants to each of the fuel cell stacks making up the fuel cell power plant.
With the forgoing problems and concerns in mind, it is the general object of the present invention to provide a fuel cell power plant having an integrated manifold system which overcomes the above-described drawbacks.
It is an object of the present invention to provide a fuel cell power plant with an integrated manifold system.
It is another object of the present invention to reduce the complexity and cost of a fuel cell power plant.
It is another object of the present invention to equip a fuel cell power plant with a common fuel or oxidant manifold.
It is another aspect of the present invention to integrate either the fuel or oxidant manifolds of a fuel cell power plant so as to reduce the weight and volume of the fuel cell power plant as a whole.
It is another aspect of the present invention to ensure the uniform distribution of fuel and oxidant reactants to the multiple fuel cell stacks making up a fuel cell power plant.
According to one embodiment of the present invention, an integrated manifold system for a fuel cell power plant includes a first fuel cell stack and a second fuel cell stack, wherein a common manifold is adapted to be in fluid communication with the first fuel cell stack and the second fuel cell stack.
The common manifold includes a first plenum for diverting a first reactant to each of the first and second fuel cell stacks, and a second plenum for accepting the first reactant as the first reactant is exhausted from each of the first and second fuel cell stacks.
These and other objectives of the present invention, and their preferred embodiments, shall become clear by consideration of the specification, claims and drawings taken as a whole.